The fetal adrenal gland of primates is one of the largest organs in the fetus and is composed of two morphologically and functionally distinct zones. The proposed study will use a recently developed cell culture system prepared from the definitive zone and from the fetal zone of the human fetal adrenal to characterize the factors that when added to fetal adrenocortical cells in culture regulate differentiated function (steroidogenesis) and growth. The factors to be studied include purified polypeptide hormones and factors, steroids and condition medium from homoglogous organ cultures of the placental or fetal pituitary. Factors that regulate the specific steroid production of the fetal zone (Delta5-steroids) and of the definitive zone (Delta4- and Delta5-steroids) will be determined by quantitation of steroid production in cell culture as measured by radioimmunoassay and high pressure liquid chromatography. By using an enzyme assay, factors will also be identified that specifically regulate the 3Beta-hydroxysteroid dehydrogenase, Delta4,5-isomerase activity of the steroid biosynthetic pathway. The low activity of this enzyme in fetal zone cells in vivo results in the characteristic steroid production for this zone. Since study of the actively growing adrenal in utero is not possible, factors regulating fetal adrenal cell proliferation will be defined using the in vitro cell culture system. The factors will be studied in adrenal cell cultures for effects on the initiation of DNA synthesis and cell replication. The characterization of the cellular regulation of steroidogenesis and growth of fetal adrenal cell cultures will provide a basis for studies on th mechanisms of this regulation and help elucidate the mechanisms of functional zonation of the human fetal adrenal cortex in utero. These studies will increase the knowledge of fetal adrenal organogenesis which involves a coordinated interaction of differentiated function and cell growth. The characterization of human fetal adrenal growth and function is necessary to understand the role of this tissue as part of the feto-placental unit.